Echocardiography has long been used to detect pericardial effusions and has recently been proposed as a method for assessing function changes in the heart due to cardiac tamponade and constrictive pericarditis. Echocardiography will be used in these proposed studies to test five discrete hypotheses related to the hemodynamics of pericardial disease in animal models of cardiac tamponade and constrictive pericarditis: 1. Tricuspid and mitral flow velocities measured by transcutaneous Doppler echocardiography are directly related to the rate of right and left ventricular filling. This hypothesis will be tested under control circumstances and during graded cardiac tamponade and constrictive pericarditis in two porcine models, obtaining Doppler flow velocity profiles simultaneously with two-dimensional echocardiograms and hemodynamic recordings. Left ventricular volume will be measured through the diastolic filling period from the two-dimensional echocardiograms and compared to Doppler flow velocity profiles. 2. Cardiac tamponade and right ventricular collapse are associated with altered tricuspid and mitral flow velocity profiles. It is anticipated that Doppler studies in our animal model of cardiac tamponade will show relative diminution of flow velocities early in diastole and increase in flow velocity following atrial systole. 3. Constrictive pericarditis is associated with distinctive changes in tricuspid and mitral blood flow velocities. It is anticipated that Doppler studies in our animal model of constrictive pericarditis will show higher blood flow velocities early in diastole than late in diastole as compared with the control situation. 4. Acute left ventricular dilatation causes increased intrapericardial pressure and can precipitate right ventricular collapse. The aorta will be acutely constricted with a hydraulic occluder in our experimental model of cardiac tamponade to study the relationship between intra-pericardial and intra-cardiac pressure and right ventricular collapse due to cardiac tamponade. 5. Pulsus paradoxus in cardiac tamponade is associated with a shift in the relative position of the interventricular septum. Septal position during cardiac tamponade will be assessed with two-dimensional echocardiography. The long term goal of this investigation is to examine the function of the pericardium and to examine mechanisms underlying diagnostic features of cardiac tamponade and constriction pericarditis.